efi: Use the generic efi.memmap instead of 'memmap'

Guenter reports that commit:

  7bf793115dd9 ("efi, x86: Rearrange efi_mem_attributes()")

breaks the IA64 compilation with the following error:

  drivers/built-in.o: In function `efi_mem_attributes': (.text+0xde962): undefined reference to `memmap'

Instead of using the (rather poorly named) global variable
'memmap' which doesn't exist on IA64, use efi.memmap which
points to the 'memmap' object on x86 and arm64 and which is NULL
for IA64.

The fact that efi.memmap is NULL for IA64 is OK because IA64
provides its own implementation of efi_mem_attributes().

Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Jonathan Zhang <zjzhang@codeaurora.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tony Luck <tony.luck@gmail.com>
Cc: Tony Luck <tony.luck@intel.com>
Link: http://lkml.kernel.org/r/20151003222607.GA2682@codeblueprint.co.uk
Signed-off-by: Ingo Molnar <mingo@kernel.org>

drivers/firmware/efi/efi.c

@@ -623,13 +623,15 @@ char * __init efi_md_typeattr_format(char *buf, size_t size,
  */
 u64 __weak efi_mem_attributes(unsigned long phys_addr)
 {
+	struct efi_memory_map *map;
 	efi_memory_desc_t *md;
 	void *p;
 
 	if (!efi_enabled(EFI_MEMMAP))
 		return 0;
 
-	for (p = memmap.map; p < memmap.map_end; p += memmap.desc_size) {
+	map = efi.memmap;
+	for (p = map->map; p < map->map_end; p += map->desc_size) {
 		md = p;
 		if ((md->phys_addr <= phys_addr) &&
 		    (phys_addr < (md->phys_addr +